1. Field of the Invention
The present invention generally relates to a data recording/reproducing device, and more particularly to a data recording/reproducing device in which a multi-level data is recorded to a recording medium while suppressing the DC components, and the multi-level data is reproduced from the recording medium.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 2002-342941 discloses a recording medium which is provided with a wobbling of a track suitable for a high recording density.
In the recording medium, the wobbling is formed so that an FSK information bit part based on the waveform subjected to FSK modulation for an information bit and a single frequency part based on the waveform of a single frequency are made to be specified units, and such specified units are continuous. Two frequencies are used in the FSK modulation: one frequency being the same frequency as the single frequency and the other frequency being different from the single frequency. The relation between the two frequencies is arranged so that the even-numbered wave and the odd-numbered wave are contained in a certain specified period.
A multi-level data recording method which is intended to increase the recording density on a recording medium and records a multi-level data with three or more levels to the recording medium is known. In the case of optical disks, the read-out signal of multi-level data has the level fluctuations and amplitude fluctuations due to the difference in the reflective index between the optical disks and the difference in the reproducing frequency characteristics between the inner tracks and the outer tracks of one optical disk.
In the multi-level data recording method, it is likely that the read-out signal is erroneously detected as being a wrong value of the multi-level data because of the above problem when the threshold values for generating the multi-level data are fixed.
To eliminate the problem, Japanese Laid-Open Patent Application No. 2002-135121 discloses the method of modulation and demodulation of RLL (run length limited) codes in which the DC components of the codeword stream using the RLL codes are suppressed.
In the modulation/demodulation method, the modulation of input data is performed using the code group for DC level suppression in addition to the code group for multi-level data generation.
In addition, Japanese Laid-Open Patent Application No. 2003-045035 and Japanese Laid-Open Patent Application No. 2003-196934, which are assigned to the assignee of the present application, disclose the method of determination of multi-level data as the background technology related to the present invention.
If the data signal after modulation comes out in the frequencies of the servo signal band, the resulting data will affect the servo signal. To eliminate the problem, the modulation is improved by the conventional modulation method so that the data signal after modulation does not come out in the frequencies of the servo signal band.
However, the conventional method causes the efficiency of the transformation of codes to deteriorate. In the case of the multi-level data, many additional information bits are needed in order to control the low-frequency components of the signal, which causes the storage capacity of the recording medium to be decreased significantly.
Moreover, in the case of the method disclosed in Japanese Laid-Open Patent Application No. 2002-135121, the amount of redundant information is increased when the DC suppression control is increasingly performed, and there is the problem in that the storage capacity of the recording medium is decreased because of the increasing amount of the redundant information.